On account of the high gas temperatures during the combustion operation in a gas turbine, it is necessary for numerous functional components to be suitably cooled. Particularly in the region of the center section of a gas turbine in which the hot gas from the combustion chamber which originates from the combustion thermally interacts with numerous components, efficient cooling of the rotating rotor is necessary. Such cooling is typically carried out via an annulus which extends in the longitudinal direction of the rotor and into which is introduced a cooling fluid, usually compressor air, in order to also dissipate thermal energy from the annulus toward the outside by its discharge line.
In essence, two functions are assigned to the cooling fluid which is introduced into the annulus. In addition to the function of cooling of the rotor, the cooling fluid also serves for the cooling of rotor blades of the expansion turbine, wherein for this the cooling fluid is conducted out via suitable discharge lines in the rotor toward the rotor blades of the expansion turbine. For the transfer of the cooling fluid into the relevant discharge lines of the rotor it is necessary, however, that the transfer effort or entry effort at the discharge line opening is as little as possible. For this reason, the cooling fluid is in most cases introduced into the annulus via a pre-swirl system which correspondingly accelerates the cooling fluid tangentially in the direction of movement of the rotor to its surface. Ideally, the cooling fluid is brought up to circumferential speed of the rotor so that additional entry effort during transfer into the discharge line openings can be saved. For the transfer, the cooling fluid typically discharges from suitably formed swirl supply lines of the pre-swirl system, passes across the annulus in its transverse direction (perpendicularly to the longitudinal direction of the rotor) and is fed to an opening of the discharge line in the rotor.
On account of the tangential flow conditioning of the cooling fluid in relation to the surface of the rotor, the transfer of mechanical rotor power to the cooling fluid, generating heat, is also largely reduced or even prevented. When discharging from the swirl supply line, the cooling fluid therefore finds itself in a thermally conditioned state which is particularly suitable for heat dissipation on the surface of the rotor to be cooled so that the transfer of heat to the cooling fluid can be carried out efficiently on account of the local temperature drop without heating of the cooling fluid on account of the rotor-fluid friction having a significantly negative influence. In order to be able to suitably dissipate the heat losses of the rotor to the outside after corresponding heat transfer, it is necessary to be able to discharge the cooling fluid from the annulus in a controlled manner.
Such an annulus system for cooling the rotor and also for forwarding the cooling fluid into the inlet passages of the rotor is described for example in EP 1 537 296 B1. Described therein is an annulus in which cooling fluid flows into the annulus from two swirl supply lines in each case or transfers into a corresponding inlet opening of a cooling fluid discharge line in the rotor. Both swirl supply lines are designed for supplying the annulus with cooling fluid, wherein the cooling fluid is acted upon by a flow component in the tangential direction to the surface of the rotor, and wherein the first swirl supply line and the second swirl supply line are also fluidically decoupled from each other by means of a plurality of sealing elements. So as not to hinder the intended transfer of cooling fluid from the second swirl supply line into the inlet opening of the discharge line of the rotor, the invention from the prior art, however, provides to install a bypass line which enables the cooling fluid in the annulus to bypass the second swirl supply line. As a consequence of the bypass line, a comparatively lower disturbing transverse flow occurs in the region of the crossover section between the second swirl supply line and the inlet opening of the discharge line in the rotor so that an efficient transfer of cooling fluid into the rotor can be carried out.
A disadvantage of this embodiment which is known from the prior art, however, is first of all a considerably higher technical cost since the bypass line has to be built into internal casing parts of the gas turbine. Furthermore, in the case of the solution which is known from the prior art, there is also the occurrence of dead spaces which are formed between the first and second swirl supply lines and in which the rotor cooling is in the first instance carried out by convective transportation of the cooling fluid. This, however, ensures an only unsatisfactory cooling in the sections of the rotor which delimit the dead spaces, and therefore leads to high heating of the rotor in certain areas which, however, it is necessary to avoid.